The present invention relates to an improvement in sacks for the storage and transport of bulk goods, for example, road salt and artificial fertilizer for forrestry and agricultural usage.
Due to the constantly increasing costs of labor, attempts have been made in all fields to avoid manual handling of bulk goods to the greatest possible extent. With regard to artificial fertilizer, for example, attempts are made to avoid the use of units of 25 to 50 kg which are handled manually when a fertilizer spreader, which may have a capacity of a ton, is to be filled, and many experiments have been made in the attempt to provide sacks which can be filled with several hundred kg and even tons of material to be transported or stored, and which can be handled more rationally than smaller units.
However, such previously developed sacks have created more problems than they have solved. Even with the five-fold and seven-fold safety measures which are required throughout the world, with the use of such known sacks, uneven distribution of stress and strain when such sack is hoisted can lead to rupturing of the sack and the resultant safety hazard and discharge of the contents at an undesired location, with subsequent trouble and consumption of time and labor for collection, if collection is at all possible.
These known types of sacks which have a capacity of from several hundred kilograms to tons, and preferably up to 1000 kilograms, and which are usually called "large-size sacks" or "intermediate bulk containers," therefore, have been based on various ideas. One type of sack has two parallel runners at two opposing edges of the opening for suspension on a forklift support. Another known type is provided with lifting straps which are attached to the exterior of the sack. However, in addition to the expense of this embodiment, there is little to ensure that the straps will remain so precisely in place that the lifting forces will be uniformly distributed and will not be concentrated in smaller areas where they can lead to strains which exceed the tearing strength of the material. Large size sacks have also been effected in a conventional manner and in the form of a conventional sack which is manually lashed around a rod or other lifting member. Since it involves manual work, the lashing varies from sack to sack with consequent variations in the distribution of strains. It is of course possible to produce sacks which, with a great degree of safety, can contain several tons if necessary. However, an additional requirement of such sacks is that they must be inexpensive enough to be disposed of after a single use. Several of the above known types of sacks are so expensive that they must be used repeatedly, and the problem and cost of returning the sacks then arise, and it is possible that they must be reconditioned before they can be refilled.
During the development of the sack according to the present invention, scale up of bags of the type described in U.S. Pat. No. 3,358,904 was also considered. However, it was soon realized that neither the design nor the material or production methods of such bags could be adapted to the large size sack in question. Mere scale up of such bags would give sacks that not only would lack the necessary strength, but would also be unsuitable in other respects.